Many processes for fastening thermoplastic bristle tufts to thermoplastic bristle carriers are disclosed in the prior art.
U.S. Pat. No. 3,604,043 issued to Lewis on Sept. 14, 1971 discloses a tuft attachment means wherein the end portions of a group of parallel fibers are heated in a shaping mold. The fibers remain in the heater long enough to fuse, but not melt, their ends and create a self-supporting heat-sealed tuft. The fused mass is shaped to a tapering configuration so that its cross-section, as measured perpendicular to the longitudinal axis of the tuft, is less than the cross-section of the fiber bundle. The softened fused portion of the tuft is immediately inserted into a tuft hole in the brush head forcing the softened fused portion of the tuft to conform to the geometric confines of the tuft hole.
U.S. Pat. No. 4,609,228 issued to Bickel on Sept. 2, 1986 discloses several different methods for attaching bristle tufts to a brush member. One such disclosed method is to heat both the pre-fused fastening ends of the bristle tufts and the corresponding fastening locations on the brush member to the point of softening and then cause the bristle tufts to be impressed against the brush member, thereby welding the bristle tufts to the brush member. Another disclosed method is to form a mushroom in a fused end of a bristle tuft by means of a heated mold and then injection molding the brush material about the mushroom to fasten the bristle tuft to the brush member. Still another disclosed method is to form an undercut hole in the brush member and introduce the heated and softened end of a bristle bundle at high speed into the hole so that the softened end compresses and fills the hole. Still another disclosed method is to attach the bristle bundle by narrowing the outermost part of hole in the brush member by means of frictional heat, such as ultrasound or spinning the sleeves that supply and hold the bristle tufts after insertion of the bristle bundles into the holes.
U.S. Pat. No. 4,637,660 issued to Weihrauch on Jan. 20, 1987, which is hereby incorporated herein by reference, discloses a method for connecting bristles to a bristle carrier which also begins by melting the ends of bundles of bristles, thereby causing the end of each bundle to convert to a non-oriented balled form comprising a thickened portion at the fastening end of each tuft. In one embodiment, the thickened ends of the bristle bundles are pressed into the heated and melted receiving side of the bristle carrier. The melted material of the bristle carrier flows behind the thickened ends so that the craters formed by insertion of the bristle bundles are then closed by the intrusion of melted material. In another disclosed embodiment, recesses that correspond to the bristle bundle set are either preformed or formed in the bristle carrier by means of hot pins extending from a heating element. Upon melting of the receiving side of the bristle carrier, the molten material flows outwardly in annular collars extending from the receiving surface of the bristle carrier. The thickened ends of the bristle bundles are pressed into the recesses in the carrier and the molten material of the annular collars again flows behind the thickened portions of the bundles.
U.S. Pat. No. 4,988,146 issued to Weihrauch on Jan. 29, 1991, which is also hereby incorporated herein by reference, discloses a method for connecting bristles to a bristle carrier which begins by melting the fastening ends of the bristle bundles accompanied by a shortening of the length of the bundle and formation of a thickened portion. Holes in the bristle carrier are formed with an at least zonally smaller cross-section than that of the thickened portions on the bristle bundles. The thickened portions of the bundles and/or the walls of the holes in the carrier are heated to their softening temperature(s). Upon insertion of the bristle bundles, the interference of the thickened portion of the bristle bundles causes displacement of the side wall material in the carrier, forming a bulge about the opening of the hole. The bulged material of the bristle carrier is thereafter shaped by a mold to produce a smooth exposed surface on the bristle carrier.
Drawbacks associated with the aforementioned prior art joinder processes include: excessively complex machinery, excessive heating and distortion of the bristle carrier, long manufacturing cycle times due to heating and cooling large amounts of thermoplastic material, the need for excessive bristle tuft clamping forces which can cause damage to the individual bristles contained within the bristle tufts, and satisfaction of critical operating parameters such as, time, temperature, and positioning tolerance, etc.
In light of the foregoing difficulties, it is an object of the present invention is to provide a simplified method of attaching thermoplastic bristle tufts to a thermoplastic bristle carrier while employing minimal heat input and minimal material distortion.